The present invention relates to a pneumatic tire, more particularly to a studless tire having an asymmetric tread pattern capable of improving cornering performance and behavior in critical cornering on snowy/icy roads.
Essentially, a studless tire is required to have improved running performance on snowy/icy roads as a winter tire. In recent years, such a studless tire is also required to have improved running performance on dry pavements because of expansion of opportunity for running on pavements cleared of snow, reduction in snowfall period caused by global warming and the like.
Heretofore, an arrangement of tread grooves and sipes, namely a tread pattern (usually a block pattern) has been elaborated.
By increasing the rigidity of tread blocks by decreasing the number of sipes and/or the depths of sipes, performance on dry pavements may be improved. But, performance on snowy/icy roads is deteriorated. This technique therefore, can not be used.
By disposing large-sized shoulder blocks in a tread shoulder zone especially in an outboard tread shoulder zone, cornering performance on snowy/icy roads and also on dry pavements can be improved. Further, by increasing the total circumferential component of edges of shoulder blocks (block edges and sipes' edges) and making the profile of tire shoulders square than round, the lateral grip during cornering can be improved. If these techniques are employed in a studless tire, the cornering performance on snowy/icy roads and dry pavements can be improved. But, during cornering on snowy/icy roads, when exceeds critical cornering speed, sudden side skid is very liable to occur, and if once side skid occurs, it is difficult to get road grip again in a short time. Thus, the critical behavior becomes unstable.